Injector Duty Cycle Calculation

[Exploded_Muffin]

For folks more knowledgeable than me:

Do you calculate injector duty cycle per injector, an average per bank, or an average across all cylinders (PW x RPM / 1200)?

I've attached a screenshot from one of my logs with bank 1 average IDC at around 90.5% and bank 2 average IDC at around 84.5%.
The average across all cylinders is 87.5%.

My fuel pressure is good but my lambdas (and fuel trims) and IDCs are different per bank at the top of a pull.
It's normally even up till about 7400 then the separation starts and increases with RPM.
It doesn't seem to be hurting anything but wondering if anyone has seen this bank to bank imbalance?

(This is a GT500 at around 22 - 23 psi and ID1300 injectors. Also fuel line lengths and fittings into and out of each rail are even)

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[engineermike]

All modern Fords have individual cylinder fuel adjustments. At max rpm and load, the stock GT500 has a range of +5% (cyl 5) to -6% (cyl 7) so you will not see the same IPW for all cylinders. But you may notice that your pulsewidths do not follow the above numbers, which is most likely due to your rapidly changing data and slow logging rates. In order to get a better idea of what's happening, you'd have to cut the channel list down to just the 8 cylinders with the polling rate set to 0(fastest)...and even then it might not catch it accurately.

I am a little surprised the logic is allowing that much duty cycle. The GT500, gen3, and (I think) gen2 voodoo share a lot of Bosch code that limits the IDC to around 75%. I wasn't sure if others outside of gen3 had encountered this but it looks like GT500 does not.

I'm learning now how to adjust the duty cycle at which it cuts throttle, which can be pretty useful.

 

[Exploded_Muffin]

All modern Fords have individual cylinder fuel adjustments. At max rpm and load, the stock GT500 has a range of +5% (cyl 5) to -6% (cyl 7) so you will not see the same IPW for all cylinders. But you may notice that your pulsewidths do not follow the above numbers, which is most likely due to your rapidly changing data and slow logging rates. In order to get a better idea of what's happening, you'd have to cut the channel list down to just the 8 cylinders with the polling rate set to 0(fastest)...and even then it might not catch it accurately.

I am a little surprised the logic is allowing that much duty cycle. The GT500, gen3, and (I think) gen2 voodoo share a lot of Bosch code that limits the IDC to around 75%. I wasn't sure if others outside of gen3 had encountered this but it looks like GT500 does not.

I'm learning now how to adjust the duty cycle at which it cuts throttle, which can be pretty useful.

Thanks Mike!
I'll relog with a cut down channel list.

Any experience with the bank to bank fuel trim and lambda difference at WOT?
Both banks track perfectly everywhere except at WOT at 7400+ with bank 1 running progressively leaner opposite to bank 2 running progressively richer.
Swapped injectors bank to bank but no dice.
I'll smoke test the intake and exhaust system for leaks and check o2 sensors and spark plugs.

 

[engineermike]

I’ve absolutely seen that….in the case of a failed and clogged cat. It backs the airflow out of one bank and, being PD blown, has to go somewhere so it goes to the other bank. I’m guessing you don’t have cars though? How big a difference is it?

 

[cbrtrx]

Assuming it's not a failed cat that's a pretty big split and no not normal. I usually see that from a poorly setup fuel system but it sounds like your rails are run in parallel with equal length lines and fittings? Could you draw a pic of how the rails are fed?

 

[Exploded_Muffin]

I’ve absolutely seen that….in the case of a failed and clogged cat. It backs the airflow out of one bank and, being PD blown, has to go somewhere so it goes to the other bank. I’m guessing you don’t have cars though? How big a difference is it?

No cats and pretty big at the top (about 12% difference -6% B2 vs 6% B1)

Assuming it's not a failed cat that's a pretty big split and no not normal. I usually see that from a poorly setup fuel system but it sounds like your rails are run in parallel with equal length lines and fittings? Could you draw a pic of how the rails are fed?

Yeap I thought it was the fuel line setup initially and redid everything to make it perfectly even across both rails (exact same line lengths and fittings into and out of both rails) but made no difference.

Someone else with basically the same setup as my car (except he runs a Fore triple 274 pump setup vs my radium dual brushless setup) is having the exact same issue.

 

[Angrey]

The legs from your first Y to the rails are both equal length? I know it's nitpicky and OCD, but I see a LOT of fuel setups where they do not equal them out. And understandably so, unless the Y block is positioned in the center of the engine bay you're going to have to loop/coil the near side one vs a straight, equal-length run to the far side.

I'm not sure the pressure delta across that short of an 8AN length of line would be enough to explain a 5% difference (at the pressures we're contemplating here).

 

[Exploded_Muffin]

The legs from your first Y to the rails are both equal length? I know it's nitpicky and OCD, but I see a LOT of fuel setups where they do not equal them out. And understandably so, unless the Y block is positioned in the center of the engine bay you're going to have to loop/coil the near side one vs a straight, equal-length run to the far side.

I'm not sure the pressure delta across that short of an 8AN length of line would be enough to explain a 5% difference (at the pressures we're contemplating here).

Yeap both rail feed and return lines from and to the Y-blocks are within 1cm of each other in length.
Was a bitch properly fitting the feed and return Y-blocks between the rear of the supercharger and firewall.

I'll be doing some testing on the car soon to see if I can find the issue.
One tuner mentioned a possible airflow imbalance issue at higher RPM/flow volume so I'll run two pressure gauges from both banks (supercharger lid has 1/8 npt ports) and see if they have mostly the same pressure up top.
Otherwise my tuner mentioned he'd seen this a few times before on GT500s at this boost level and swapping to larger injectors (ID1700) resolved it.
I feel like bigger injectors will mask the issue vs truly resolving it and while I've already just purchased the ID1750s I'll test everything else out first and only throw them on if I don't find any issues.

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